Worms versus plastic

How caterpillars can cause polyethylene degradation

April 25, 2017 12:15 am | Updated 12:15 am IST

Polyethylene, the plastic that is toughest to be degraded, has met its match. The larvae of wax moth Galleria mellonella have been shown to degrade polyethylene into ethylene glycol at an unbelievably fast rate.

In a paper (“Polyethylene biodegradation by caterpillars of the wax moth Galleria mellonella” ) published on April 24 in the journal Current Biology , Federica Bertocchini from the Institute of Biomedicine and Biotechnology of Cantabria, Spain, and her team found that worms kept in a polyethylene shopping bag formed holes in about 40 minutes. In about 12 hours, nearly 100 wax worms kept in the bag reduced the mass of plastic by 92 mg. About 2.2 holes were made per worm per hour.

To confirm that the breakdown of polyethylene was not due to chewing, the researchers meshed the caterpillars and applied the paste on a polyethylene film. Compared with films that were not treated with the paste, there was 13% loss of mass at the end of 14 hours in the case of the film treated with the paste. Though the loss of mass using the paste is less than when the worms were in direct contact with polyethylene film, the average degradation rate of 0.23 mg per cm per hour is “markedly higher” than what was reported earlier.

Spectroscopic analysis carried out by the researchers showed that untreated parts of the film showed signatures of polyethylene while the treated parts of the film carried ethylene glycol signature, thus confirming the biodegradation of polyethylene into ethylene glycol.

Further studies showed that parts of the film that were treated with the paste had greater surface roughness, suggesting that the physical contact of the paste changed the integrity of the polymer surface. “It was a chance discovery,” Dr. Bertocchini told The Hindu . “I am a beekeeper and was clearing the beehives as they were infested with worms. I put the worms in a plastic bag. But soon I found the bag was full of holes and the worms were outside the bag.”

It is possible that one or more enzymes of the caterpillar is causing the degradation, she says.

Wax worms live as parasites in bee colonies. They lay their eggs inside the hives which then hatch and grow eating the beeswax. There is a lot of similarity in the chemical structure of polyethylene and beeswax. The caterpillars are breaking down the chemical bonds of polyethylene like they do to the beeswax, she says.

The team is planning to isolate the molecules involved in the degradation and study the efficiency of degrading polyethylene into ethylene glycol.

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